The trend in modern telecommunication switching systems has been to provide flexible data services as well as providing voice services. In particular, proposals have been made for an integrated services digital network (ISDN) arrangement in which customers can exchange data as well as voice communications over the same facility. Data and voice communications in proposed ISDN arrangements are generally arranged to be sent in packets and to use the packet switching protocols of the X.25 and X.31 standards adopted by the Consultative Committee on International Telephone and Telegraph (CCITT) for communications between a terminal and a connected ISDN switch.
The protocols used for transmitting packetized data in proposed ISDN arrangements are layered according to the Open Systems Interconnection (OSI) Model of the International Standards Organization (ISO). The bottom or first layer, the physical layer, defines the type of electrical signal which is transmitted over a facility. Layer 2 is used for communicating packetized data over a link from a terminal to a data network or node, or over a link between data nodes. The third layer, used for communicating with a data network, conveys addressing data defining a path. Higher layers also exist but are not pertinent to this discussion.
For data communications, it is very important that reliable transmission be attained in which virtually all transmitted data packets are delivered without errors, checked for the proper order of arrival, and acknowledged. The packet switching protocols or basic rules for providing reliable data communications at different layers provide a high degree of flexibility so that the total volume of data traffic over a network may be optimized under a variety of traffic conditions.
A result of this high degree of flexibility is that each frame of a packet, which must traverse many links within a data network before reaching its destination, is repeatedly subjected to extensive data processing. This data processing introduces substantial delay in the transmission of a data packet from its source to destination and heavily uses specialized resources which perform such data processing, called protocol handlers, within each node of a data network.
A problem of the prior art therefore exists in that there is no satisfactory arrangement for achieving minimum delay and minimum protocol handler resource utilization in the transmission of customer data packets through data networks while maintaining the high level of reliability characteristic of international data transmission protocols.